1. Field of the Invention
This invention relates to a method and apparatus for supplying foam to tanks using mounted foam generators and foam solution supply lines.
2. Background
When tanks are filled with crude oil or other chemicals which have a substantial vapor pressure, a continuing problem is the loss of light hydrocarbon or other vapors from the tank during filling. The vapors are lost primarily because the liquid filling the tank forces the vapors above the liquid from the tank, thereby forcing the vapors into the atmosphere. Inert gas has been used to prevent the formation of explosive mixtures in the tank by filling the tank with inert gas prior to filling the tank. The use of such inert gas does not prevent the loss of vapors of the liquid filling the tank from escaping into the atmosphere. If the liquid charged to the tank has a relatively high vapor pressure, then vapors from the liquid filling the tank will pass into the gas phase in the tank long before the tank is filled so that the gases emitted from the tank as the liquid level rises will contain substantial quantities of vapors resulting from the vaporization of the liquid filling the tank. It has been very difficult to find effective methods for preventing the discharge of this vapor from the tank. Various attempts have been made to pass the vapor to alternate tanking, recovery or treatment facilities and the like.
This problem is more acute when loading tankers with crude oil. The crude oil is frequently warmer than the ambient air when loaded into the tankers since crude oil is frequently transported at an elevated temperature. As well known to those skilled in the art, crude oil represents a large number of separate components, many of which are volatile at room temperature. These materials tend to vaporize from the crude oil, especially at elevated temperatures. Further, large volumes are loaded into and discharged from tankers during the transportation of crude oil. The vaporous materials lost during such loading are valuable hydrocarbon fuels that cannot be economically recovered for use as hydrocarbon fuels. Nevertheless, the control of this discharge is of great concern because of the undesirable discharge of benzene into the atmosphere. As a result, considerable effort has been directed to the development of improved methods for eliminating or controlling the discharge of vaporous hydrocarbons during the loading of crude oil tankers.
Previously, it has been proposed that the use of warm, inert gas will reduce the amount of hydrocarbon vapors lost during loading of tankers. Such an approach is shown in U.S. Pat. No. 5,054,526 entitled "Method and System for Reducing Hydrocarbon Vapor Emissions From Tankers", issued Oct. 8, 1991 to Thomas K. Perkins and assigned to Atlantic Richfield Company.
An earlier proposal shown in U.S. Pat. No. 3,850,206 entitled "Foamed Vapor Barrier", issued Nov. 26, 1974 to Garold P. Canevari and William M. Hooper, Jr. and assigned to Exxon Research and Engineering Company, uses a foamed barrier in the crude oil cargo area to control the release of vapors from the crude oil. It is proposed that the foam will ordinarily be supplied through existing openings in the deck which are frequently used for the cleaning apparatus.
U.S. patent application No. 07/653,398 entitled "Method for Controlling Vapor Emissions During Loading of Tankers", filed Feb. 11, 1991 by Thomas K. Perkins, now U.S. Pat. No. 5125439, discloses a process for supplying foam to tanks in a crude oil tanker prior to loading the crude oil by generating the foam at a central source and thereafter passing it through lines usually used for the loading of crude oil to produce a foam layer in the tanks in the tanker prior to loading the crude oil.
A variety of foams are known for controlling vapors from hazardous spills as shown in Report No. PB87-145660 "Handbook for Using Foams to Control Vapors from Hazardous Spills" Science Applications International Corporation, McLean, Virginia, prepared for the Environmental Protection Agency, Cincinatti, Ohio, July 1986 and in PB82-227117 "Evaluation of Foams for Mitigating Air Pollution from Hazardous Spills" MSA Research Corporation, Evans City, Pa., prepared for Municipal Environmental Research Lab, Cincinnati, Ohio, Feb. 1982.
U.S. Ser. No. 07/584,978 entitled "High Stability Foams for Long Term Suppression of Hydrocarbon Vapors", filed Sep. 19, 1990 by Kenneth Miller, Karen Schultz and Sophany Thach, and U.S. Ser. No. 07/908299 (a continuation of U.S. Ser. No. 07/584,978) entitled "High Stability Foams for Long Term Suppression of Hydrocarbon Vapors", filed Jul. 2, 1992 by Kenneth Miller, Karen Schultz and Sophany Thach (PCT/US 91/06795) disclose desirable foams for use in controlling the release of hydrocarbon vapors from crude oil.
In U.S. Ser. No. 07/653,398, it is disclosed that when foam is introduced into tanks on a tanker according to the existing commercial operation, the foam is dispensed through a foam generator which is mounted on a special Butterworth cover which closes a hatch at the top of the compartment. The generator is suspended into the compartment at the top and mixes a surfactant solution with the inert gas present in the compartment to form the foam. The foam exits the generator and falls into the bottom of the compartment to form a layer thereon before the crude oil is loaded through a loading manifold. The use of the in situ generator adds substantially to the capital cost of this system and its placement in the plurality of tanks is time-consuming and substantially increases the time for loading a tanker.
Accordingly, a continuing effort has been devoted to the development of methods for controlling and minimizing the release of hydrocarbon vapors from tanks during filling of the tank with liquids which release vapors.